JP-2009-85164A (US-2009-0088951A1) shows a fuel injection system which is provided with a fuel pressure sensor detecting a fuel pressure in a fuel passage between a common-rail and an injection port of a fuel injector. Based on a detection value of the fuel pressure sensor, a fuel pressure waveform indicative of a variation in fuel pressure due to a fuel injection is detected. Since the actual injection-rate variation can be computed based on the fuel pressure waveform, an operation of a fuel injection is feedback controlled based on the actual injection-rate variation.
Furthermore, in the above fuel injection system, when a computed injection-rate variation significantly deviates from a specified value, a computer of the system determines that a malfunction, such as clogging of a fuel injector occurs.
In this fuel injection system, although the computer determines whether a malfunction of fuel injection exists, it can not be identified which portion is defective. For example, when a fuel leaks from a common-rail, it is likely that both of the common-rail and the fuel injector may be replaced new ones, notwithstanding that the fuel injector is not faulty.